Foundries produce metal castings using a sand casting process. The sand casting process is characterized by using sand as a mold material. A frame or mold box known as a flask contains the molding sand. A foundryman creates mold cavities by compacting molding sand around mold patterns within the flask. The metal casting is formed by filling the mold cavities with molten metal. Most metals shrink upon cooling. To prevent the shrinkage from creating voids in the metal casting, a reservoir known as a riser is built into the mold. Risers provide molten metal to the casting as it solidifies so that any voids form in the riser and not the casting.
Foundries are sometimes faced with the situation where the amount of space between a mold cavity and the top of the mold is insufficient to allow for a correctly sized riser. A correctly sized riser contains enough molten material to compensate for any shrinkage in the casting. The height to diameter ratio of the riser varies depending on the molten material, location of the riser within the flask, and the size of the flask. When the space available between the mold cavity and the top of the mold will not accommodate the calculated riser size, foundrymen have traditionally followed the time and labor intensive process of abutting a riser sleeve to the exterior of the flask.
In the traditional process, a foundryman inserts a short section of riser sleeve between the pattern and the top of the mold. After the mold is complete, the foundryman adds an additional riser sleeve to the outside of the flask and abutting the top of the molded riser sleeve. To prevent molten metal from leaking at the abutment, the foundryman packs molding sand around the junction of the external riser sleeve and the molded riser sleeve. After the molding process is complete and before the flask may be reused, the foundryman must clean the flask exterior of any molding sand and any metal that may have leaked through the junction between the molded riser sleeve and the external riser sleeve during casting. Such leakage during casting may also result in a defective casting because of an insufficient volume of molten material available to the mold cavity. Additionally, the molding sand packed around the junction between the external riser sleeve and the molded riser sleeve sometimes migrates through the junction, contaminating the mold cavity.